There have been a few studies showing that they save money by better controlling temperature based on time and season. They also start heating or cooling the home in advance of your set time. So say if you have set your thermostat to be at 68 degrees at 7 AM, and 58 before, they will figure out how long it takes to heat to 68 and start the furnace/heat pump at the right time to hit 68 at 7 AM.
I've installed multiple thermostats, they are very easy to do.
The previous owner put in 2 American Standard heat pumps in 2016 with their corresponding company thermostats. I don't have any issues with the AS thermostats as they are programmable, have the filter reminder and do everything except the wifi connection. One of the things I like about the Google Nest is that it senses when no one is home and automatically adjusts the temp. As retirees we don't have that typical 9-5 work schedule away from home that I can program into the thermostat but for the impromptu trips to the store or wherever if the thermostat can do its thing without manual intervention every time we go to somewhere that'd be pretty sweet.
I agree with you about the ease of swapping thermostats out. Being in our old place for 35 years I replaced a few of them. For a standard AC unit there were only 4 color coded wires which made things easy peasy. This is my first time fiddling with a heat pump but I believe there are 5 wires.
